I don't have the mini yet but when I get it the mini will have more games and entertainment apps whereas my phone will be used for cellular service and act as an ipod with all my music (my ipad will have music on it too)
Since my 5s is 32 gigs, I just keep everything on there and still have more than half the space available, loving it. On My mini I just keep some photos games and e-books. Only 16 gigs so kind of limited.
I've now got my music and photos on my 64 GB iPad mini, and my 32 GB iPhone 5S has iTunes Match. I use them in very different ways, but always keep them both near.